Vertically aligned liquid crystal display

ABSTRACT

Disclosed is a liquid crystal display comprising a first substrate made of an insulating material; pixel electrodes formed on the first substrate, the pixel electrodes having a first aperture pattern; a second substrate made of an insulating material and provided opposing the first substrate at a predetermined distance; a common electrode formed on the second substrate, the common electrode having a second aperture pattern; and a liquid crystal layer made of liquid crystal material that is injected between the first and second substrates, wherein either or both of the pixel electrodes and the common electrode include stepped portions that protrude a predetermined distance away from the substrates, between apertures of the first and/or second aperture patterns.

BACKGROUND OF THE INVENTION

[0001] (a) Field of the Invention

[0002] The present invention relates to a vertically aligned liquidcrystal display, and more particularly, to a vertically aligned liquidcrystal display having a aperture pattern formed in electrodes to obtaina wide viewing angle.

[0003] (b) Description of the Related Art

[0004] A liquid crystal display (LCD) is structured having liquidcrystal injected between an upper substrate having a common electrodeand a color filter, and a lower substrate having thin film transistorsand pixel electrodes. A voltage of a different potential is applied tothe pixel electrodes and common electrode to form an electric field,thereby varying the alignment of liquid crystal molecules of the liquidcrystal material. In this way, the transmittance of incident light iscontrolled to display images.

[0005] In a vertically aligned (VA) LCD, long axes of the liquid crystalmolecules align themselves vertically to the substrates in a state whereno electric field is formed between the substrates. The VALCD has a highcontrast ratio and a wide viewing angle such that this LCD configurationis the most commonly used type of liquid crystal display.

[0006] In one method to obtain a wide viewing angle in the VA LCD,aperture patterns are formed in the electrodes. With this configuration,a fringe field is used to uniformly scatter a slanting direction of theliquid crystal molecules into four directions to achieve a wide viewingangle. A conventional VA LCD, having aperture patterns formed in theelectrodes to obtain a wide viewing angle, will now be described withreference to FIG. 1.

[0007]FIG. 1 shows a partial sectional view of a conventional VA LCDhaving aperture patterns formed in electrodes.

[0008] A pixel electrode 110 is formed on an insulating lower substrate100, and a common electrode 210 is formed on an insulating uppersubstrate 200. Aperture patterns are formed in the pixel electrode 110and the common electrode 210. Apertures of the aperture pattern of thepixel electrode 110 are provided alternately with apertures of theaperture pattern of the common electrode 210. Further, liquid crystalmaterial is injected between the substrates 100 and 200 to form a liquidcrystal layer 300.

[0009] As shown in the drawing, a fringe field generated by the aperturepatterns uniformly controls a slanting direction of liquid crystalmolecules of the liquid crystal layer 300. A wide viewing angle isrealized as a result. However, at center portions between apertures ofthe upper substrate 200 and the lower substrate 100, weak fringe fieldforms an area by the vertical electric field with respect to thesubstrates where the liquid crystal molecules do not quickly changealignments by the electrical field. Also, the liquid crystal moleculesin these areas begin to slant only after liquid crystal molecules in thevicinity of the aperture patterns are slanted. This slows down theresponse speed of the LCD.

SUMMARY OF THE INVENTION

[0010] The present invention has been made in an effort to solve theabove problems.

[0011] It is an object of the present invention to provide a verticallyaligned liquid crystal display in which a lower and an upper aperturepattern are formed in electrodes of at least one substrate to form astepped pattern at the center of the aperture pattern. Accordingly, aresponse speed is improved.

[0012] To achieve the above object, the present invention provides aliquid crystal display comprising a first substrate made of aninsulating material; pixel electrodes formed on the first substrate, thepixel electrodes having a first aperture pattern; a second substratemade of an insulating material and provided opposing the first substrateat a predetermined distance; a common electrode formed on the secondsubstrate, the common electrode having a second aperture pattern; and aliquid crystal layer made of liquid crystal material injected betweenthe first substrate and the second substrate, wherein either or both ofthe pixel electrodes and the common electrode include stepped portions,which protrude a predetermined distance away from the substrates,between apertures of the first and/or second aperture patterns.

[0013] According to a feature of the present invention, the pixelelectrodes include the stepped portions.

[0014] According to another feature of the present invention, thestepped portions are formed by providing the pixel electrodes over agate insulation layer and a protection layer.

[0015] According to yet another feature of the present invention, thecommon electrode includes the stepped portions.

[0016] According to still yet another feature of the present invention,the pixel electrodes include first stepped portions and the commonelectrode includes second stepped portions.

[0017] According to still yet another feature of the present invention,the first stepped portions and the second stepped portions are providedin a sequence of the first aperture pattern, the second steppedportions, the first stepped portions, and the second aperture pattern.

[0018] According to still yet another feature of the present invention,the liquid crystal display further comprises thin film transistorsformed on the first substrate, the thin film transistors switching imagesignals transmitted to the pixel electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate an embodiment of theinvention, and, together with the description, serve to explain theprinciples of the invention:

[0020]FIG. 1 is a partial sectional view of a conventional verticallyaligned liquid crystal display;

[0021]FIG. 2 is a partial sectional view of a vertically aligned liquidcrystal display according to a first preferred embodiment of the presentinvention;

[0022]FIG. 3 is a combination sectional view and transmissivity graphcomparing the vertically aligned liquid crystal display of the firstpreferred embodiment of the present invention with a conventionalvertically aligned liquid crystal display; and

[0023]FIG. 4 is a partial sectional view of a vertically aligned liquidcrystal display according to a second preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Preferred embodiments of the present invention will now bedescribed in detail with reference to the accompanying drawings.

[0025]FIG. 2 shows a partial sectional view of a vertically alignedliquid crystal display according to a first preferred embodiment of thepresent invention.

[0026] A pixel electrode 11 is formed on a lower substrate 10, the lowersubstrate 10 being made of an insulating material such as glass, and acommon electrode 21 is formed on an upper substrate 20, which is alsomade of an insulating material. A first aperture pattern P1 and a secondaperture pattern P2 are formed respectively in the pixel electrode 11and the common electrode 21. Apertures of the first aperture pattern P1are provided alternately with apertures of the second aperture patternP2. Plateaus 14 are formed on the lower substrate 10. The pixelelectrode 11 is formed over the plateaus 14 such that stepped portionsare formed. The plateaus 14 are formed by a gate insulating layer 12 anda protection layer 13.

[0027] The stepped portions start at roughly a center between an edge Aof the apertures of the first aperture pattern P1 and an edge B of theapertures of the second aperture pattern P2, that is at areas C. Since afringe field is also formed by the stepped portions, the liquid crystalmolecules positioned over areas C quickly respond to a generatedelectric field.

[0028] In a liquid crystal display, many more elements than thosedescribed above are provided on the lower and upper substrates 10 and20. For example, additionally provided on the lower substrate 10 aregate wiring, data wiring, and thin film transistors, and additionallyprovided on the upper substrate 20 are a color filter and a blackmatrix.

[0029] The gate wiring transmits scanning signals, the data wiringtransmits image signals, and the thin film transistors act as aswitching element to either transmit or cut off the image signals to thepixel electrode 11 according to the scanning signals. These elements donot appear in the drawing to simplify the explanation of the firstembodiment.

[0030]FIG. 3 shows a combined sectional view and transmissivity graphcomparing the vertically aligned liquid crystal display of the firstpreferred embodiment of the present invention with a conventionalvertically aligned liquid crystal display.

[0031] In FIG. 3, it is to be assumed that a drive voltage be appliedafter a threshold voltage of 1.7 V is applied for 150 msec. Shapes ofequipotential lines and alignment of liquid crystal molecules are shownin the lower part of FIG. 3, while the curved lines of the upper part ofFIG. 3 are transmissivity curves, in which the changes are with respectto time.

[0032] As shown by area B of the conventional LCD, in which no steppedportion is provided, light transmissivity slowly decreases with time atareas between the apertures of the aperture patterns. On the other hand,in the present invention having stepped portions, the liquid crystalmolecules at areas between the apertures of the aperture patterns arealigned simultaneously with the liquid crystal molecules at edges of theapertures as a result of the transformed electric field due to thestepped portions.

[0033] Accordingly, with reference to area A, a light transmissivity isnearly identical throughout the liquid crystal display of the presentinvention, thereby enhancing response speed.

[0034] Table 1 below shows a comparison between response speeds of theconventional LCD and the LCD of the present invention at different graylevels. TABLE 1 Starting Applied Present Difference in voltage (V)voltage (V) Prior art (ms) invention ms time ms 1.7 2.5 147 123 24 3.080 64 16 3.5 47 38 9 4.0 32 25 7 5.0 16 13 3 2.0 2.5 120 100 20 3.0 6758 10 Average 72.7 60.14 12.56

[0035] As shown in Table 1, the present invention has a response speedat all gray levels that is faster than the conventional LCD. Ofparticular interest is the improvement in response speed of between 20and 25 ms at low gray levels.

[0036]FIG. 4 shows a partial sectional view of a vertically alignedliquid crystal display according to a second preferred embodiment of thepresent invention.

[0037] A pixel electrode 11 is formed on a lower substrate 10, the lowersubstrate 10 being made of an insulating material such as glass, and acommon electrode 21 is formed on an upper substrate 20, which is alsomade of an insulating material. A first aperture pattern P1 and a secondaperture pattern P2 are formed respectively in the pixel electrode 11and the common electrode 21. Apertures of the first aperture pattern P1are provided alternatingly with apertures of the second aperture patternP2. Plateaus 14 are formed between the pixel electrode 11 and the lowersubstrate 10, and plateaus 22 are formed between the common electrode 21and the upper substrate 20. As a result, stepped portions are formed onthe lower and upper substrates 10 and 20. The plateaus 14 of the lowersubstrate 10 are formed of a gate insulating layer 12 and a protectionlayer 13.

[0038] The stepped portions of the lower substrate 10 and the uppersubstrates 20 start at a center area between an edge A of the aperturesof the first aperture pattern P1 and an edge B of the apertures of thesecond aperture pattern P2. That is, areas C, at which point the steppedportions of the lower substrate 10 begin to form, are misaligned withareas D, at which point the stepped portions of the upper substrate 20begin to form.

[0039] By forming the stepped portions also on the upper substrate 20,the further increased effects of varying the electric field improve theresponse speed.

[0040] In the LCDs of the present invention described above, steppedportions are formed only on the lower substrate and on both the upperand lower substrates. However, it is also possible to form protrudingareas only on the upper substrate. A detailed description of such aconfiguration will be omitted, as such modifications will be well knownto one of ordinary skill in the art.

[0041] In the present invention, the response speed of the liquidcrystal display is improved by forming stepped portions betweenapertures of the lower substrate and the upper substrate. That is, bythe transformed electric field resulting from the stepped portions, theslanting direction of the liquid crystal molecules is better controlledin areas between the apertures to enhance the overall response speed.

[0042] Although preferred embodiments of the present invention have beendescribed in detail hereinabove, it should be clearly understood thatmany variations and/or modifications of the basic inventive conceptsherein taught which may appear to those skilled in the present art willstill fall within the spirit and scope of the present invention, asdefined in the appended claims.

What is claimed is:
 1. A liquid crystal display, comprising: a firstsubstrate made of an insulating material; pixel electrodes formed onsaid first substrate, said pixel electrodes having a first aperturepattern; a second substrate made of an insulating material and facingsaid first substrate at a predetermined distance; a common electrodeformed on said second substrate, said common electrode having a secondaperture pattern; and a liquid crystal layer made of liquid crystalmaterial injected between said first substrate and said secondsubstrate, wherein at least one of said pixel electrodes and said commonelectrode include a stepped portion, which protrudes a predetermineddistance away from the substrates, between the first aperture patternand the second aperture pattern.
 2. The liquid crystal display of claim1, wherein said pixel electrodes include the stepped portion.
 3. Theliquid crystal display of claim 2, wherein the stepped portion is formedby providing the pixel electrodes over a gate insulation layer and aprotection layer.
 4. The liquid crystal display of claim 1, wherein saidcommon electrode includes the stepped portion.
 5. The liquid crystaldisplay of claim 1, wherein said pixel electrodes include a firststepped portion and said common electrode includes a second steppedportion.
 6. The liquid crystal display of claim 5, wherein the firststepped portion and the second stepped portion are provided in asequence of the first aperture pattern, the second stepped portion, thefirst stepped portion, and the second aperture pattern.
 7. The liquidcrystal display of claim 1, further comprising a thin film transistorformed on said first substrate, the thin film transistor switching imagesignals transmitted to the pixel electrode.